In the slitter-winders of paper and board machines a web is cut in the cross-direction into several component webs, and a pair of blades comprising a top blade and a bottom blade is used in the cutting. The width of the component webs to be slit by the blades and thus the position of the slitting blades can vary to a great extent when different blade settings are used, depending on the set widths of the rolls to be produced. The slitting blades have to be positioned, in the lateral direction of the web, in the right slitting position corresponding to the desired roll widths. In order to produce component webs of the desired width the slitting blades of the slitter-winder are spaced apart as desired in the lateral direction of the paper or board web i.e. a change of settings is carried out.
FI patent 68185 discloses a method and a system for position change. This publication describes a method in a system used in the slitting of a paper web, in which, to observe the position of the slitting device, a measuring device is used which is in a position arrangement which comprises actuating members for controlling and performing the movement of the measuring device in the cross-direction of the web and which system comprises at least one limiter i.e. for limiting the operation of the measuring device along the distance between the extreme positions such that one extreme position serves as the datum position for the determination. An observing device in both directions of movement observes at least one member of the slitting device. The system comprises drive means for the actuating members and moving devices performing a corrective movement of a movable device or member. The position of the slitting blades has been determined during a standstill of the machine by means of this known arrangement, having the aim of minimizing the duration of the standstill.
It is known from prior art to measure the position of the blades used in slitting by means of a carriage-type arrangement, in which a sensor is placed in a moving carriage with which, by means of optic or magnetic measurement, the position of the blades has been established. These measurement methods are used in connection with the changing of settings.
In a prior art application based on magnetic measurement each blade carriage is equipped with a fixed permanent magnet, and the distance between the permanent magnet and the slitting blade is constant, and the position of the permanent magnet connected to the blade carriage is measured by means of a magnetic measuring device, thereby establishing the position of the blade. In connection with the changing of blade settings, information is also needed, in addition to the information on the position of the sharpening blades, on the new, replacing blades and, after the detachment and grinding of the blades, position information, since, after these steps, the distance between the slitting blade edge and the magnet of the blade carriage changes, which means that no exact information on the position of the blade is available based on the results from the measurement methods described above. Also, the slitting blade edge wears, which leads to inaccuracy when using the above-mentioned measurement methods. In the above-described situations, when prior art applications have been used, there has been a need to carry out so-called tuning runs in order to determine the position of the slitting blade edge.